Scroll-Type Fluid Machine

ABSTRACT

A scroll-type fluid machine in which: a fixed scroll and a moveable scroll are disposed in a housing; a fluid pocket, the volume of which varies, is formed between the fixed scroll and the moveable scroll; and a thrust plate for receiving the reaction force in the axial direction of pressure applied within the fluid pocket is disposed between the bottom plate of the moveable scroll and the housing. The scroll-type fluid machine is characterized in that at least the surface of the thrust plate facing the bottom plate of the moveable scroll is subjected to tin plating. As a consequence, it is possible to efficiently produce, at a low cost, a thrust bearing which is disposed between the bottom plate of the moveable scroll and the housing, exerts excellent seizure resistance, and has a high PV limit level and a low friction coefficient.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a scroll-type fluid machine, andspecifically relates to an improvement of a thrust bearing interposedbetween a movable scroll bottom plate and a housing.

BACKGROUND ART OF THE INVENTION

In a scroll-type fluid machine such as a scroll-type compressor and ascroll-type expander, it is usual that a thrust bearing member forreceiving an axial reaction force, such as a compression reaction force,to an inner pressure of a fluid pocket formed between a fixed scroll anda movable scroll is provided between a bottom plate of the movablescroll which revolves around the fixed scroll as being prevented fromrotating and a housing. The thrust bearing member may be a thrust platemade with a ring-shaped plate member. Such a thrust plate and such abottom plate of the movable scroll are required to have an excellentseize resistance as well as a high PV limit level and a low coefficientof friction which are enough to prevent both members from adhering toeach other.

With respect to such a requirement, Patent document 1 discloses astructure where a steel thrust bearing for receiving a thrust load isprovided between a movable scroll member and a front housing and thebottom plate surface at the side of the movable scroll is tinned inorder to improve an abrasion resistance and a seize resistance. Patentdocument 2 discloses a structure where solid lubricant coating is formedon either of the outside of a movable scroll end plate or a slidingsurface of a trust bearing to slide the end plate, or both.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: JP8-247052-A

Patent document 2: JP8-061256-A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the structure disclosed in Patent document 1, because a certain partof the movable scroll having a complicated shape is tinned, some partsmust be masked or few number of movable scrolls can be put at a time inthe plating barrel, so as to cause problems such as poor productivityand high cost.

In the structure disclosed in Patent document 2, there might be aproblem, that the forming cost of the solid lubricant coating is highand a sufficiently high seize-resistance load is not obtained because ofless adhesion of the coating. In order to improve the adhesionperformance, it is possible that a chemical treatment such as a chemicalconversion treatment or a physical treatment such as a shot blasting isprocessed between the thrust plate base material and the coating layer.However, both treatments may cause a high cost.

Accordingly, an object of the present invention is to provide ascroll-type fluid machine which achieves excellent seize resistance,high PV limit level and low coefficient of friction with a low cost anda good productivity.

Means for Solving the Problems

To achieve the above-described object, a scroll-type fluid machineaccording to the present invention is a scroll-type fluid machine inwhich a fixed scroll and a movable scroll to revolve around the fixedscroll as being prevented from rotating are provided to a housing, afluid pocket having a variable volume is provided between the fixedscroll and the movable scroll, and a thrust plate to bear an axialreaction force of a pressure applied into the fluid pocket is providedbetween a bottom plate of the movable scroll and the housing,characterized in that at least a surface of the thrust plate facing thebottom plate of the movable scroll is plated with tin-based metal. Herethe tin-based metal for plating includes tin alloy, as well as a singlemetal of tin.

In such a scroll-type fluid machine, a simple ring-shaped plate of thethrust plate is plated with tin, so that a simple masking would beenough even if a masking is required in the plating process. Therefore,the plating can be achieved at a low cost. Further, because the thrustplate is a member which has a simple structure and is smaller than themovable scroll, more number of thrust plates can be put at a time in theplating barrel. With such a good operability and a good productivity,the plating can be achieved at a low cost. Furthermore, even compared toa solid lubricant coating film, a plated layer having a high adhesionperformance can be realized at a low cost. Additionally, because thethrust plate is plated with tin, a good sliding performance is ensuredbetween the thrust plate and the bottom plate of the movable scrollwhich faces thereof, and the sliding surface is improved in itsconformability so as to prevent defect such as a seizing between thescroll and the thrust plate. As a result, the seize resistance can begreatly improved at this part, so as to obtain a high PV limit and a lowcoefficient of friction, and therefore the durability can be greatlyimproved.

In the present invention, it is possible that a base material of thethrust plate is made of iron-based steel plate, cast metal or lightmetal. The light metal may be aluminum, aluminum alloy, magnesium alloy,or titanium alloy. The iron-based steel plate or the cast metal makes itpossible that the productivity is improved. The light metal cancontribute to the weight saving of the fluid machine.

It is possible that the thrust plate is provided with a base layerplated with the tin-based metal. The base layer makes it possible thatthe tin-based metal for plating adheres much better. The base layer forplating may be a nickel plating or a copper plating.

It is preferable that the base layer (a surface before plating) platedwith the tin-based metal on the thrust plate has a predetermined surfaceaspect. Concretely, it is preferable that a skewness Rsk defined byFormula 1 is less or equal to −0.05 and a kurtosis Rku defined byFormula 2 is more or equal to +2.5, wherein the skewness Rsk and thekurtosis Rku are prescribed in JISB0601 (corresponding to InternationalStandard: ISO4287) concerning surface roughness. It is more preferablethat the skewness Rsk is less or equal to −0.1 and the kurtosis Rku ismore or equal to +3.0. If the skewness Rsk and the kurtosis Rku are insuch preferable range, desirably high PV limit and desirably lowcoefficient of friction can be achieved at the same time. Details of theskewness Rsk and the kurtosis Rku will be explained later. In order tosatisfy the predetermined range of the surface aspect, the followingsurface processing method may be employed. The base material of thethrust plate is processed by cutting with a lathe, and then is processedby a finish grinding process, so as to be shaped with a predeterminedsurface roughness. In order to improve the surface roughnesspractically, it is preferable that the material is processed by a barrelfinishing process according to the barrel finishing method after thegrinding. The barrel finishing can easily form a surface having apredetermined surface roughness.

$\begin{matrix}{{Rsk} = {\frac{1}{{Rq}^{3}}\left\lbrack {\frac{1}{lr}{\int_{0}^{lr}{{Z^{3}(x)}\ {x}}}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where, Z(x) is a function showing a profile and Rq is a root-mean-squareheight of the profile

$\left( \sqrt{\frac{1}{l}{\int_{0}^{l}{{Z^{2}(x)}\ {x}}}} \right).$

$\begin{matrix}{{Rku} = {\frac{1}{{Rq}^{4}}\left\lbrack {\frac{1}{lr}{\int_{0}^{lr}{{Z^{4}(x)}\ {x}}}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

where, Z(x) is a function showing a profile and Rq is a root-mean-squareheight of the profile

$\left( \sqrt{\frac{1}{l}{\int_{0}^{l}{{Z^{2}(x)}\ {x}}}} \right).$

It is preferable that tin-based metal to be plated with has a thicknessof 1-15 μm. The thickness is more preferably 2-12 μm, and furtherpreferably 3-10 μm. If the thickness is set within such ranges, the tincomponent filled in the valleys on the plate surface makes up for thesurface conformability even in a case where several parts of the tinnedlayer of the thrust plate surface have been exfoliated. If the thicknessof tinned layer is less than 1 μm, the tinned layer might not besufficiently formed in valleys of the surface of base material, andtherefore, the superficial conformability is not easily ensured and thelubrication might deteriorate. On the other hand, if the thickness oftinned layer is more than 15 μm, the loss of tinned layer mightfluctuate the dimension in an axial direction of the compressor, so thatthe compressor functionality might be not maintained even if thelubrication is ensured.

The plating method is not limited to a specific method. For example,electroplating or non-electrolytic plating can be employed. It ispossible that a masking is performed before the plating process.Alternatively, in order to simplify a preparation operation, it ispossible that a whole surface of the thrust plate is plated with thetin-based metal.

It is possible that the thrust plate is formed in a ring-shaped solidplate, and alternatively is formed in a plurality of members dividedcircumferentially, which is divided into two half-ring-shapedpartitions, for example. It can be designed arbitrarily from a viewpointof workability in assembling, etc.

The structure of the scroll-type fluid machine according to the presentinvention is applicable to both a scroll-type compressor and scroll-typeexpander. The present invention is applicable to a scroll-type fluidmachine for vehicles, and specifically to a scroll-type compressor forvehicles, which strongly requires a high durability and a long life, andis suitable to a scroll-type compressor in an air-conditioning systemfor vehicles.

Effect According to the Invention

A scroll-type fluid machine according to the present invention makes itpossible that the sliding surface of the thrust plate plated with atin-based metal improves the conformability and the movable scroll andthe thrust plate are prevented from adhering to each other, so that ahigh PV limit level and a low coefficient of friction are achieved. Ahigh productivity can also be achieved because the cost can be reducedfrom a conventional process, such as a film coating with a solidlubricant and a tin plating on a scroll side.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a longitudinal section view of a scroll-type compressor as ascroll-type fluid machine according to an embodiment of the presentinvention.

FIG. 2 shows thrust plates, where (A) is a plan view of the thrust plateof the scroll-type compressor in FIG. 1, (B) is a schematic side viewthereof and (C) is a schematic side view of a thrust plate according toanother embodiment.

FIG. 3 shows a thrust plate according to another embodiment, where (A)is a plan view and (B) is a schematic side view.

FIG. 4 is a comparison chart of PV limit among various layered films ina sliding test.

FIG. 5 is a comparison chart of coefficient of friction among variouslayered films in a sliding test.

FIG. 6 is a relationship chart of skewness Rsk and PV limit.

FIG. 7 is a relationship chart of kurtosis Rku and PV limit.

FIG. 8 is a characteristic chart of surface roughness, showing anexample of surface aspect shift caused by skewness Rsk shift.

FIG. 9 is a characteristic chart of surface roughness, showing anexample of surface aspect shift caused by kurtosis Rku shift.

FIG. 10 is a schematic superficial section view of a thrust plate,showing an example of surface aspect shift before and after slidingwhile only skewness Rsk is in a specific range.

FIG. 11 is a schematic superficial section view of a thrust plate,showing an example of surface aspect shift before and after slidingwhile skewness Rsk and kurtosis Rku are both in each specific range.

FIG. 12 is a schematic superficial section view of a thrust plate,showing an example of surface aspect shift caused by tinned platethickness shift.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments will be explained as referring tofigures.

FIG. 1 shows a scroll-type compressor 1 as a scroll-type fluid machineaccording to an embodiment of the present invention. In this embodimentof scroll-type compressor 1, a housing is provided with fixed scroll 4and movable scroll 5 which revolves around fixed scroll 4 in a stateprevented from rotating between front housing 2 and rear housing 3, andfluid pocket 6 of which volume is varied is formed between fixed scroll4 and movable scroll 5. Accompanying movable scroll 5 swinging, sealedfluid pocket 6 is moved radially toward the center, so that the volumeof fluid pocket 6 is reduced so as to compress the fluid, such asrefrigerant, in fluid pocket 6. Tip seals 7 are attached to the tipparts of scroll walls of fixed scroll 4 and movable scroll 5, so as tocontribute the sealing during compression movement. The compressed fluidis discharged through a discharge hole perforated at the central part ina radial direction of fixed scroll 4 to discharge chamber 8, and then isdelivered to the outside through discharge port 9. Movable scroll 5revolves as swinging in a condition where its rotation is prevented by arotation preventing mechanism having rotation preventing pins 10.Movable scroll 5 is driven with eccentric bush 11 which is rotatablypositioned on the back side of its bottom plate 5a, and main shaft 12which is eccentrically engaged with eccentric bush 11 as being rotatablerelatively. Main shaft 12 is supported by front housing 2 through drivebearing 13 rotatably. The rotary driving force of main shaft 12 istransmitted through pulley 14 and electromagnetic clutch 15 from anexternal drive source (not shown).

Ring-shaped thrust plate 21, which receives an axial reaction force tothe pressure applied into fluid pocket 6, is provided between bottomplate 5 a of movable scroll 5 and front housing 2. Thrust plate 21 andbottom plate 5 a of movable scroll 5 move as sliding on each other,accompanied by the swing movement of movable scroll 5. Thrust plate 21is plated with tin-based material at least on a surface facing bottomplate 5 a of movable scroll 5.

Thrust plate 21 is configured to be a ring-shaped solid plate member asshown in FIG. 2(A), and is plated with tinned layer 22 on the surfacefacing bottom plate 5 a of movable scroll 5 of thrust plate basematerial 21 a as shown in FIG. 2(B). The surface plated with tinnedlayer 22 is supposed to be sliding surface 23 to slide on bottom plate 5a of movable scroll 5. Though FIG. 2(B) shows an embodiment where thrustplate base material 21 a is plated with tinned layer 22 only on thesurface facing bottom plate 5 a of movable scroll 5, it is possible thatthe tin-plating is applied to both surfaces or all over thrust platebase material 21 a from a viewpoint of the workability in plating andthe treatment efficiency, etc. Alternatively, an interlayer such as baselayer 24 of tinned layer 22 may be formed between thrust plate basematerial 21 a and tinned layer 22, as shown in FIG. 2(C). Base layer 24may be a layer plated with nickel or copper, as described above. Baselayer 24 can make tinned layer 22 improve in adhesion. Plated layers canbe formed by electroplating or non-electrolytic plating.

The thrust plate may be formed in a ring-shaped solid plate shown inFIG. 2(A) as well as a plurality of members divided circumferentially asshown in FIG. 3(A) and 3(B). In FIG. 3, thrust plate 31 consists of twopartitions. Each thrust plate base material 31 a is plated with tinnedlayer 32, and the surface plated with tinned layer 32 is supposed to besliding surface 33 to slide on bottom plate 5 a of movable scroll 5. Thenumber of partitions can be designed arbitrarily from a viewpoint ofworkability in assembling and plating, and treating efficiency, etc.

With such a tinned thrust plate, specifically with thrust plates of twokinds of which one is tinned and the other is tinned with Nickel-platedbase layer, the sliding test results of PV limit and coefficient offriction are shown in FIGS. 4 and 5 which are comparison charts of PVlimit and coefficient of friction among various layered films in asliding test as compared with resin-coated layer. The test has beenconducted as a ring-on-plate test, where the circumferential velocity is6 m/s and the surface pressure is 6 MPa, under a lubricating atmosphere.As shown in FIG. 4, PV limit levels of both a tinned layer and a tinnedlayer with a Ni-plated base layer are higher than that of a resincoating. Further, as shown in FIG. 5, coefficients of friction of boththe tinned layer and the tinned layer with a Ni-plated base layer arestably lower than that of the resin coating for a long time.

As described above, it is preferable that skewness Rsk defined by theabove-described Formula 1 is less or equal to −0.05 and kurtosis Rkudefined by the above-described Formula 2 is more or equal to +2.5,wherein parameters prescribed in JISB0601 (corresponding toInternational Standard: ISO4287) concerning surface roughness aredetermined for the surface aspect of a base layer (surface which has notbeen plated yet) of the tinned layer of the thrust plate. It is morepreferable that skewness Rsk is less or equal to −0.1 and kurtosis Rkuis more or equal to +3.0. The above-described ranges of skewness Rsk andkurtosis Rku have been specified so as to achieve PV limit more or equalto 20 MPa·m/s, as much as an appropriate sliding performance isexpected. Namely, such parameter ranges are specified as ranges toachieve PV limit more or equal to 20 MPa·m/s, while the relationshipbetween skewness Rsk and limit PV and the relationship between kurtosisRku and PV limit are shown in FIGS. 6 and 7.

With FIG. 8 and FIG. 9, skewness Rsk and kurtosis Rku can be moreclearly understood in their concept. As shown in FIG. 8, when skewnessRsk is less or equal to −0.05, peak widths increase and the surface areabecomes greater. Therefore, because the contact area to slide on themovable scroll increases, the surface pressure load bearing can beincreased. On the other hand, when skewness Rsk is less or equal to−0.05, it is difficult to obtain high sliding performance, because thenumber of valleys decreases so that tin filled in valleys is not enoughto keep lubrication. Even in such a condition, when kurtosis Rku is moreor equal to 2.5, peaks of the roughness profile become sharper so as toform sufficiently many valleys as shown in FIG. 9. Therefore tin andother lubrication components can be held to enhance lubrication.Consequently a high sliding performance can be achieved. Thus, thethrust plate base material having a surface roughness, where skewnessRsk of less or equal to −0.05 and kurtosis Rku of more or equal to 2.5,is tinned, so that the contact area increases to improve the surfacepressure load capacity and that the number of the surface valleysincreases to fill a large number of the surface valleys with conformabletin plating component, so as to achieve highly enhanced lubrication andsmall coefficient of friction.

Further, if such a surface aspect is achieved, even in a case whereseveral parts of the tinned layer of the thrust plate surface have beenexfoliated, it is possible that tin filled in the surface valleys makesup for the conformability of the surface. Thus, even if the skewness Rskof the base material surface is less or equal to −0.05, the lubricationmight deteriorate because the number of valleys decreases as shown inFIG. 10 so as not to exhibit good superficial conformability by tinfilled in the valleys, in spite of its great width. Accordingly, if asurface aspect, such that skewness Rsk is less or equal to −0.05 andkurtosis Rku is more or equal to 2.5 or less, is ensured as shown inFIG. 11, the number of valleys increases, so that tin filled thereindevelops sufficient superficial conformability as well as lubricationretention.

Further, it is preferable that thickness of the tinned layer is 1-15 μm,as described above. It is more preferably 2-12 μm, and is furtherpreferably 3-10 μm. Such designed thickness, such as around 5 μm as thethickness of tinned layer 42 on base material 41 shown in FIG. 12(B),makes it possible that tin filled in valleys on the surface sufficientlymakes up for the conformability of the surface, even in a case whereexfoliation of the tinned layer of the thrust plate surface hasprogressed. As shown in FIG. 12(A), if the thickness of tinned layer 42is less than 1 μm, the tinned layer might not be sufficiently formed invalleys of the surface of base material 41, and therefore, thesuperficial conformability is not easily ensured and the lubricationmight deteriorate. Further, as shown in FIG. 12(C), if the thickness oftinned layer 42 is more than 15 μm, the loss of tinned layer 42 mightfluctuate the dimension in an axial direction of the compressor (platethickness direction), so that the compressor functionality is notmaintained even if the lubrication is ensured.

Furthermore, in order to confirm the above-described ranges aspreferable conditions, the ring-on-plate sliding test has been conductedunder lubrication atmosphere in various conditions of thrust plates. Thetest has been conducted while the circumferential velocity has beenconstant and the surface pressure has been gradually increased at aconstant speed. Here, PV limit is defined as a product ofcircumferential velocity (V) and surface pressure (P) at a time when thecoefficient of friction suddenly increases (when coefficient of frictionbecomes more or equal to 0.03). The criteria are the following.

PV limit: o (Good); if the level is more or equal to 20 MPa·m/s, x (NoGood); otherwise

Coefficient of friction: o (Good); if the level is less than 0.04, x (NoGood); otherwise

The results are shown in Table 1 and Table 2.

TABLE 1 Surface Sliding performance roughness Plating CoefficientDetermination Rsk Rku thickness PV limit of friction PV Coefficient [μm][μm] [μm] [MPa · m/s] [—] limit of friction Example 1 −1.66 6.76 5.4 440.03 ∘ ∘ Example 2 −0.42 3.25 2.5 38 0.03 ∘ ∘ Comparative −0.13 1.46 5.122 0.06 ∘ x Example 1 Comparative 0.22 2.13 4.3 16 0.04 x x Example 2Comparative 1.12 1.53 6.8 11 0.06 x x Example 3

TABLE 2 Surface roughness Plating Determination Rsk Rku thickness SeizeCoefficient [μm] [μm] [μm] resistance of friction Example 1 −1.66 6.765.4 ◯ ◯ Comparative −1.32 4.12 0.8 X ◯ Example 1 Comparative −2.13 3.120.5 X X Example 2

As shown in Table 1 and Table 2, it has been confirmed that thepreferable conditions according to the present invention can achieveboth of desirable high PV limit and low coefficient of friction.

Industrial Applications of the Invention

The structure of a scroll-type fluid machine is applicable to any of ascroll-type compressor and a scroll-type expander, and is suitable to afluid machine for vehicles which strongly requires a high durability anda long life. Above all it is suitable to a scroll-type compressor forvehicles, and is specifically suitable to a scroll-type compressorprovided in an air-conditioning system for vehicles.

Explanation of Symbols

1: scroll-type compressor

2: front housing

3: rear housing

4: fixed scroll

5: movable scroll

5 a: bottom plate of movable scroll

6: fluid pocket

7: tip seal

8: discharge chamber

9: discharge port

10: rotation preventing pin

11: eccentric bush

12: main shaft

13: drive bearing

14: pulley

15: electromagnetic clutch

21, 31: thrust plate

21 a, 31 a: thrust plate base material

22, 32: tinned layer

23, 33: sliding surface

24: base layer

41: base material

42: tinned layer

1. A scroll-type fluid machine in which a fixed scroll and a movablescroll to revolve around the fixed scroll as being prevented fromrotating are provided to a housing, a fluid pocket having a variablevolume is provided between the fixed scroll and the movable scroll, anda thrust plate to bear an axial reaction force of a pressure appliedinto the fluid pocket is provided between a bottom plate of the movablescroll and the housing, characterized in that at least a surface of thethrust plate facing the bottom plate of the movable scroll is platedwith tin-based metal.
 2. The scroll-type fluid machine according toclaim 1, wherein the thrust plate is made of iron-based steel plate,cast metal or light metal.
 3. The scroll-type fluid machine according toclaim 1, wherein the thrust plate is provided with a base layer platedwith the tin-based metal.
 4. The scroll-type fluid machine according toclaim 3, wherein the base layer is a nickel plating or a copper plating.5. The scroll-type fluid machine according to claim 1, wherein the baselayer plated with the tin-based metal on the thrust plate has a skewnessRsk defined by Formula 1 which is less or equal to −0.05 and a kurtosisRku defined by Formula 2 which is more or equal to +2.5, wherein theskewness Rsk and the kurtosis Rku are prescribed in JISB0601(corresponding to International Standard: ISO4287) concerning surfaceroughness. $\begin{matrix}{{Rsk} = {\frac{1}{{Rq}^{3}}\left\lbrack {\frac{1}{lr}{\int_{0}^{lr}{{Z^{3}(x)}\ {x}}}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$ where, Z(x) is a function showing a profile and Rq is aroot-mean-square height of the profile$\left( \sqrt{\frac{1}{l}{\int_{0}^{l}{{Z^{2}(x)}\ {x}}}} \right).$$\begin{matrix}{{Rku} = {\frac{1}{{Rq}^{4}}\left\lbrack {\frac{1}{lr}{\int_{0}^{lr}{{Z^{4}(x)}\ {x}}}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$ where, Z(x) is a function showing a profile and Rq is aroot-mean-square height of the profile$\left( \sqrt{\frac{1}{l}{\int_{0}^{l}{{Z^{2}(x)}\ {x}}}} \right).$6. The scroll-type fluid machine according to claim 1, wherein thetin-based metal to be plated with has a thickness of 1-15 μm.
 7. Thescroll-type fluid machine according to claim 1, wherein a whole surfaceof the thrust plate is plated with the tin-based metal.
 8. Thescroll-type fluid machine according to claim 1, wherein the thrust plateis formed in a plurality of members divided circumferentially.